Many liquid compositions, any of which hereinafter may be called "baths" for brevity, even though they may be used by spraying or other methods of establishing contact than immersion, are known for the purpose of treating tinned surfaces. The liquids disclosed, for example, in Japanese Patent Kokai H1-100281 are known as surface treatment liquids for tin-plated DI cans. These surface treatment liquids are chemical film forming liquids for the treatment of metal surfaces which contain from 1 to 50 grams/liter (hereinafter usually abbreviated as "g/L") of phosphate ions, from 0.2 to 20.0 g/L of oxyacid ions, from 0.01 to 5.0 g/L of tin ions and from 0.01 to 5.0 g/L of condensed phosphate ions, and in which the pH is from 2 to 6. Furthermore, surface treatment agents which have further improved surface treatment operability have been disclosed in Japanese Patent Kokai H6-173024. It is possible by treating tin-plated DI cans with these conventional chemical treatment agents to form a phosphate film which has excellent corrosion resistance of the surface of the tin-plated DI cans. However, there is a problem in that no improvement of mobility is observed with these phosphate based films. Furthermore, there has been a trend in recent years to reduce the amount of tin-plating on tin-plated DI cans, for reasons of economy, and surface treatment which has much better corrosion resistance than in the past is required for such lightly tin-plated DI cans.
On the other hand, if the outer surface of the cans has a high friction coefficient, in the can production process, slip failure between can surfaces may occur during the conveyor transportation of a large number of metal cans, so that the cans move sideways, and this leads to problems with transportation. The transportability of the cans is a particular problem when the cans are being moved into a printer. Hence, it is necessary to reduce the friction coefficient of the outer surface of the cans without having an adverse effect on the adhesion properties of the paint, printing ink(s) or lacquer which is to be coated on the outer surface of the can. The method disclosed in Japanese Patent Kokai S64-85292, for example, is known as a means of improving the mobility. A surface treatment agent for metal cans which contains water soluble organic materials selected from among phosphate esters, alcohols, mono- or poly-basic fatty acids, fatty acid derivatives and mixtures of these materials is used in this method. However, although an improvement in the mobility is achieved by this method, there is a problem in that there is often inadequate improvement in corrosion resistance and/or paint adhesion properties.
Furthermore, the methods disclosed in Japanese Patent Kokai S61-91369, Japanese Patent Kokai H1-172406, Japanese Patent Kokai HI-177379, Japanese Patent Kokai H1-177380, Japanese Patent Kokai H2-608 and Japanese Patent Kokai H2-609, for example, are known as methods for the surface treatment of metals in which water soluble polymers are used, with a view to providing the metal surface with corrosion resistance and adhesive properties. With these conventional methods the metal surface is treated with a solution which contains derivatives of polyhydric phenol compounds. However, with these conventional methods it is difficult to form a film which has adequate stability on the metal surface, so that satisfactory corrosion resistance often is not obtained. Also, there is still a problem in that satisfactory paint adhesion is not always obtained even with the method of treatment disclosed in Japanese Patent Kokai H4-187782 which is an improved method of treatment which includes the above-mentioned derivatives of polyhydric phenol compounds.